1. Field of the Invention
The present invention relates to a method of treating waste. In another aspect, the present invention relates to a method of treating waste containing pathogens. In still another aspect, the present invention relates to a method of treating waste containing pathogens to render the waste suitable for ultimate disposal.
2. Description of the Related Art
One of the major problems facing society today is the processing and the disposal of waste. The term waste includes, as typical examples, garbage and related domestic wastes, raw human wastes, solid industrial wastes, packaging materials, plastics, glass and metal containers, sludges of various types and sources, slags and other materials occurring as wastes in the metallurgical or mining industries, chemical process by-products not economically utilizable and oil materials. Compounding the problem is the ever increasing amount of wastes of all kinds being produced. In addition, nearly all pollution control processes result in the production of solids, sludges, or liquids with a higher concentration of pollutants than originally existed in the waste stream. Also, some wastes are the result of other waste treatment processes, and some are unwanted or non-recycled process by-products.
Packaging materials, garbage, and other combustible matter may be disposed of in part by incineration, but this in itself involves problems such as the evolution of air pollutants, including toxic substances, from the incinerators, the costs of moving the waste to the incinerators, emission of objectionable odors, and the disposal of the incinerator residues. In addition, at the present time, incineration is not always a politically viable alternative for disposal of waste.
Other major sources of waste products include disposable items as women's wear, aprons, towels, and particularly, hospital items including gowns, disposable bedding, disposable items used for mass feeding in institutions, baby diapers, and adult incontinent wear.
Non-combustible wastes, such as glass and metal containers, and non-biodegradable plastics are obviously more difficult to dispose of than are combustible wastes.
As for human wastes, as late as 1945, it was the accepted practice of many municipalities to dispose of human waste by flushing or dumping the waste into bodies of water with reliance upon the dissolved oxygen content of the water to effect biological purification. With the development of the concepts of environmental control, there was increasing public condemnation of such pollution of streams and lakes which resulted in the development of methods, such as the activated sludge process, of treating municipal sewage that are less subject to objection.
Such wastes as garbage, metallurgical slag, glass and metal containers, and other municipal and industrial solid waste have been used for many years as landfill. To some extent this disposition of such solid waste has been successful but it has likewise resulted in secondary pollution and health problems, and land so reclaimed may not in any event be suitable for certain purposes, such as building construction, because of the unstable nature of the filled land. That is, some types of solid wastes are physically or chemically unstable. Thus, garbage decomposes under the influence of natural factors, with release of objectionable odors, toxic or biologically harmful products which enter into the contiguous water table and make their way into nearby streams, thus creating a water pollution problem.
Moreover, experience has shown that even with the best so-called sanitary landfills there can also result insects, rodents, and disease problems, and even air pollution in the form of odors or smoke from refuse fires. Inevitable decomposition of non-permanent materials results in reduction of the volume of material used as landfill with resultant subsidence of the filled land. Subsidence can also occur when metals are gradually corroded with volume reduction, and this is exaggerated in the case of large hollow objects such as automobile bodies, metal cans, and drums. The burning of worn out automobile tires creates hugh volumes of objectionable, sooty smoke, and even if such tires are buried there may be a tendency for them to rise to the surface of the filled land after a period of time. Moreover, even if the subsidence referred to does not occur, land so filled may be insufficiently compacted or stable to support various types of structures.
U.S. Pat. No. 3,837,872 issued Sep. 24, 1974 to Connor addressed some of the deficiencies with traditional landfill methods. The '872 process concerns treatment of sewage sludge and other wastes by chemical fixation and physical entrapment of pollutants. The waste is treated by mixing it with a setting agent and silicate. The resulting product is a friable, clay-like mass having a polymer lattice that entraps and prevents migration of toxic materials such as heavy metals and some organics.
Unfortunately, typical sewage contains a broad variety of pathogens such as bacteria, fungi, viruses, parasites, and protozoans. If significant amounts of pathogens are present, use of such material as landfill, fertilizer or erosion material can be dangerous.
The U.S. Environmental Protection Agency (EPA) has recognized the problems which disposal of pathogen infested waste can present. In response to these problems, the EPA has issued guidelines at 40 C.F.R. .sctn. 257 concerning land disposal of sewage sludge which contains pathogens. The EPA regulations recognize three separate categories of sludge: unstabilized sludge, sludge exposed to a process to significantly reduce pathogens (PSRP), and sludge exposed to a process to further reduce pathogens (PFRP). "Unstabilized sludge" has not been exposed to any pathogen reducing process, is not suitable for land disposal, and can only be incinerated, buried or heat dried. Sludge which undergoes a PSRP, such as anaerobic digestion, heat treatment, lime stabilization, or air drying can be disposed on land only if public access to the land is controlled for a period of from twelve to eighteen months. Finally, sewage which has undergone a PFRP has no disease related restrictions on reuse. Unfortunately, to destroy some parasites, such as the ascarid, PFRP methods require either expensive, highly energy intensive processes such as radiation or thermal processing which are generally unsuitable for transforming the sewage sludge into a readily reusable end product, or if utilizing lower energy levels, require longer processing times. The ascarid is a helminth worm that is a common parasite in the intestines of humans and animals. Particularly susceptible to helminthiasis (intestinal infestation with helminth) are ruminants such as sheep, cattle, goats, pigs, horses, and mules. A wide variety of anti-helminthic agents have been discovered, and they have varying degrees of efficacy.
Among the classes of materials which are known to be toxic to helminth such as ascarid (Ascaris fuum, Alumbricoibes) are the two substituted benzimidazoles of U.S. Pat. No. 3,325,356, phosphoramidates of U.S. Pat. No. 4,269,829, acetyl and carbalkoxythioureidobenzophenones of U.S. Pat. No. 4,310,537, and avermectin and milbemycin compounds of U.S. Pat. No. 4,547,491. Such compounds, however, are intended for therapeutic use in individual animals and are unsuitable for general addition to sewage sludge.
Ammonia is also known to be toxic to ascarides. For example, Tropical Diseases Bulletin, Vol. 76, No. 3, Abstract 556, and Helminthological Abstract Series A, Vol. 45, No. 11 (1976), Abstract 5830 and Vol. 47, No. 3, Abstract 1272, disclose that treatment of sewage with 3-4% ammonia by volume destroys all visible ascarides present. Reducing the ammonia concentration to 2%, however, left many of the eggs viable.
Other researchers have found that relatively high volumes of ammonia are toxic to ascarides. Part of the problem encountered by the researchers, however, has been that ammonia evaporates and reduces the concentration of toxic ammonia present to combat ascarides.
Reimers et al, U.S. EPA Publication No. 600/S2/81/166 (October 1981), Order No. PB 82-102 344 discloses that conventional sludge treatment processes (mesophilic and anaerobic or aerobic digestion) are not very effective in destroying parasite eggs, and ammonification studies of ascarides were inconclusive. In another study, Reiners et al found that when ammonium sulfate at a dosage of 50 milligrams ammonia per gram of sludge was added to sludge previously aerobically digested at 25.degree. C. for ten days, there was little effect on the ascarid eggs during the first five days. After ten days, 62% of the eggs were inactivated. When the ammonia concentration was increased to 500 milligrams per gram solids, complete or near complete inactivation was observed after ten days. When ammonia gas was added to sludges previously aerobically digested at 25.degree. C. at detention times of 10, 20, or 30 days, a dosage of 1% ammonia was necessary to obtain effective inactivation of the ascarid eggs. See, U.S. EPA Publication No. 600/S1/185/022 (January 1986 ) Order No. PB86-135 407/AS.
A serious problem with ammonification of sewage sludge is that a large enough amount of ammonia must be added to the sludge to kill ascarides within a reasonable period of time. It was previously thought that at least 2% ammonia by volume was required to effectively destroy most viable ascarides in sludge within ten days. If the sludge was not sealed in an airtight reaction vessel, however, additional amounts of ammonia were required to compensate for volatilization.
U.S. Pat. No. 4,793,927, issued Dec. 27, 1988 to Meehan et al discloses that the above described '872 patent process does reduce viability of ascarid eggs in sewage sludge by the highly alkaline environment of the chemical fixation process which hydrolyses nitrogen containing waste in the sludge to evolve some ammonia to kill some ascarid eggs. It is stated that the '872 process, however, still leaves about 60% of the ascarid eggs viable. Waste containing such a high percentage of viable ascarid eggs fails to satisfy environmental regulations for substantial elimination of parasites from treated sludge which is to come into contact with humans or their food chain. For safety and in order to qualify as a PFRP, at least about 99.9% of viable parasites must be destroyed. The level of indicator pathogens in a spike sample must be reduced by three logs. Such a test is designed to ensure that actual municipal sludge treated with the process will substantially eliminate all the parasites, and the '872 process would not qualify.
The '927 patent describes the '872 process as effective in satisfying the EPA requirements for a PFRP with respect to bacteria and viruses, because the highly alkaline environment produced by the '872 process is toxic to bacteria and viruses, reducing their total coliform at least three logs such that less than 0.1% of them survive the treatment.
To improve upon the '872 process, the '972 patent discloses a method of treating sewage which includes the steps of mixing the sewage with a source of material toxic to parasites, preferably an ammonia source, and forming a substantially and permeable mass from the mixture of sewage and source of toxic material. In a preferred embodiment, the mixture of sewage and ammonia source are formed into an impermeable mass by mixing the sewage with a silicate and a setting agent in sufficient proportion to form a substantial and permeably mass.
While the '927 process does overcome the major deficiency of the '872 process with respect to the ascarid eggs, the '927 process itself suffers from several major deficiencies. First, the reaction between the setting agent, the silicates and the waste produce a matrix structure whose structural strength needs improving. Second, due to the nature of the reaction and the temperatures achieved in the reaction, an objectional amount of ammonia is retained in the waste, such that if it is used as landfill, objectionable amounts of ammonia may be detected at the surface of the landfill. Finally, both the '872 and the '927 processes produce a treated product that comprises 35-40% solid. Many environmental regulations require a solids content of at least 50% if not higher. Of course this solids content can be achieved by, for example, evaporation but will require more time and/or energy to achieve such a solids content.
Therefore, there is a need for a waste treatment process that will produce a stronger waste product, having a reduced amount of retained ammonia, and having a higher solids content.